OA11262A

OA11262A - Bearing device

Info

Publication number: OA11262A
Application number: OA9900255A
Authority: OA
Inventors: Leif Bohlin
Original assignee: Global Hemostasis Inst Mgrab
Priority date: 1997-05-26
Filing date: 1999-11-24
Publication date: 2003-07-30
Also published as: EP0983450A1; DE69825747T2; ATE274149T1; CN1095947C; WO1998054475A1; SE9701959D0; JP2002502484A; EP0983450B1; DE69825747D1; CA2291791A1; AU7682398A; CN1258339A; US6218751B1

Abstract

Bearing device of magnet type for instruments and the like and non-contact support of one part relatively to another part by means of magnet fields wherein the one part is rotatable relatively to the other at least a part of a full turn. The novelty lies therein that the magnet devices intended to keep the rotatable part essentially centered relatively to the stationary part are off-set so that besides radially acting force components also axial force components biasing the rotatable part in an axial direction appear; and in that a connection device connecting the rotatable part with the stationary part and permitting the former to turn at least a portion of a turn is arranged along the axis of rotation so as to keep the rotatable part correctly off-set positioned.

Description

BEARING DEVICE 5 Technical field of the invention

This invention relates to bearing devices with extremely low friction for the usefor instance in rheological measuring devices and other sensitive instruments. io Background of the invention in a known measuring instrument a movable instrument part is suspended bymeans of and between vertical tapes or strings with low torsion résistance andhaving low starting torque. The movable instrument part is to be influenced by is the power, the effect or the like to be measured. The moving coil galvanometeris one example of such an instrument. Instrument parts suspended by tapes orstrings may be used for instruments where the displaceable or rotatable part isinfluenced or biased without physical contact, i.e. without mechanical influencefrom another part. For purposes where the object to be tested or otherwise 20 analysed is to be physically attached to the movable part or where an indicatingdevice or the like is to be mechanically connected to a transmitter the knownarrangements are hardly usable.

It has been suggested to use - for bearings where low friction and low starting 25 torque is required - different types of magnetic bearings. DE 34 37 937 discloses a such device and more in detail a device for guiding and supportingrheological measuring Systems. The intention was to bring about, in a simpleway, a guiding and supporting arrangement with minimum friction and based onone stationary and one mobile magnet System with a soft iron part arranged with 30 a vertical air gap.

Already in the 19th century however it was proved by a Mr.EARNSHAW that a devices like the one according to the DE publication is functionally impossible 01126, because of their inhérent instability. It is physically impossible to achieve stabilityboth axially and radially as is maintained in the DE publication. The deviceaccording to the DE publication not oniy has inferior latéral stability but is alsounstable which means that it will collapse and loose its position either at theupper or the lower pair of magnets immediately.

To further clarify the state of the art and to define the invention over the State ofthe art, it must be mentioned that the invention is based primarily on passivemagnet Systems including permanent magnets only. Active magnet bearingsinclude electromagnets shaped and arranged in a way very similar with thearrangement of a stator of a synchronous motor, whereas the armature or rotornormally is formed by a circular package of transformer sheet métal. Theposition of the rotor is read and checked by means of a number of distancesensors the signais from which via a quick acting boost control System optimisesand distributes signais to each of the amplifier each controlling aneiectromagnet. In this way the rotor and shaft can be easily re-set and guided toits intended position. Annular magnet bearings, often called passive magnetbearings include annular shaped permanent magnets which attract alternativelyrepel each other in such a way that stability is achieved in one desired directiononly, radially or axially. In the other direction, however, the bearing will always r be unstable, a fact which was proven more than a hundred years ago. If everutilized, this type of bearings always is used together with an auxiliary bearingsuch as an active magnéto bearing.

Aspects on the invention

One purpose with the invention is to bring about, by utilising a passive magnetSystem having a minimum of frictional résistance, an axially and radially stablebearing device especially but not exclusively for instruments of rheometer type. 3 ΟΊI26,

Summary of the invention

The invention is a bearing device for passively supporting one part movablerelatively to another part by means of magnets, preferably permanent magnetsin order to bring about a stable essentially friction free measuring of a torque in arange where conventional bearing Systems of the instrument bail bearing type orthe like hâve too high a friction and too high a starting torque and thecharacterising features of the invention lies in that at one part and at anotherpart, the one part rotatable relatively to the other part at least part of arévolution, pairs of magnet units arranged in a repulsion or attraction state arepositioned regarding their fields of force in such a way that force componentshold the rotatable part in a predetermined radial position and bias the rotatablepart in an axial direction and in that at least one mechanical, essentially stablepositioning means is connected between the one part and the other part andacting along the axis of rotation for counterbalancing the force biasing the onepart in the one axial direction.

Brief description of drawings

In the following the invention will be described more in detail with references tothe attached drawing, in which,

Figure 1 is a schematically axial section showing one embodiment of the bearingdevice with passive magnet bearings utilised for a viscosimeter of Couette type,Figure 2 is a schematically axial section of an embodiment with a passivemagnet bearing device utilised for an oscillating viscosimeter,

Figure 2b is a schematically axial section through an embodiment with a passivemagnet bearing device arranged with axially magnetised concentric magnets fora viscosimeter having including a cup,

Figure 2c in an axial section shows an oscillating viscosimeter with only a cupand an embodiment of a passive magnet bearing arranged with radiallymagnetised concentric magnets, ΟΊ Ί26,

Figure 3 shows in an axial cross section a viscosimeter of Couette type withrépulsive magnet bearings with passive magnets arrangée! in a parallel state,Figure 4 in a same way illustrâtes an oscillating viscosimeter with an attractivepassive magnet bearing with the magnets arranged in parallel, and 5 Figure 5 schematically shows ten different configurations with combinations ofradially and axially magnetised magnétos acting as a radial magnéto bearing,Figure 6 schematically partly in cross section shows a rheological instrumentwith a bearing according to the invention, and

Figure 7 is a longitudinal sectional view of a further embodiment. 10

Detailed description of preferred embodiments

As an example of field of use has been selected viscometers especially suchones for rheometer purposes and the viscosimeter is in the drawings symbolised 15 by a vessel marked K. The viscometers are very schematically illustrated andthe purpose is to establish that a measuring is to take place with a mediuminside the vessel K enclosing and surrounding a central measuring body M. Thebearing device naturally can be used for other types of instruments withrotational movements less than a full circle. 20

In ail the embodiments shown, there is at least one pair of magnet unitsincluding one stationary magnet unit 1 and at least one movable magnet unit 2and the magnet units are concentrically arranged relatively to an axis aroundwhich one instrument part is rotatable. The shown magnets units hâve ail 25 permanent magnets, but it is theoretically possible to replace the magnets ofthe one pair with electromagnets. Normally several pairs of magnet unitscooperate with each other.

The stationary magnet units 1 are arranged or affixed at a stationary part, such 30 as a support or stand 3 only schematically shown, whereas the movable magnet units 2 are arranged at or affixed to a rotatable part, such as a body or spindle rotatable relatively to the support or stand 3. The two parts are connected by 5 01 1 26 means of a connecter 5 permitting relative rotation over at least part of arévolution and the purpose of this will be further discussed below.

The pairs of magnet units 1 and 2 and their fields of force are so arrangedrelatively to each other that by means of the interaction the one or rotatable part4 is kept centred relatively to the other or stationary part 3. This can be reachedby means of repulsion of attraction. On arranging any pair of magnet units tointeract there exists between the interacting fields of force - in a defined relativeposition - a so called null point, i.e. a relative position where a sort of equilibriumprevails. This equilibrium, however, is extremely unstable and even a tinymechanical disturbance causes the interaction to collapse resulting in andisplacement of the relative positions of the parts involved.

According to this invention the interacting magnet units with their fields of forceare positioned relatively to each other off-set from the null point, meaning thatthere appear, besides the essentially radial force components working formutually repulsing or attracting the parts, i.e. keeping the rotatable part centredrelatively to the stationery part, also axial forcecomponents which bias therotatable part in the one axial direction or the other, depending on in whichdirection relatively to the off-set point the parts are displaced. By arrangingbetween the one or rotatable part 4 and the other or stationary part 3 theconnecter means 5 the axial biasing force is counterbalanced and the position ofthe rotatable part, both radially and axially relatively to the stationary partremains stable.

The connecter means shown in Figures 1-4 is a so called torsion means, viz. astring or tape which allows rotation over at least part of a révolution and normallyseveral révolutions with a minimum résistance.

It is also possible to use, in stead of the torsion means, string or tape taking up a tensional force, a connecter means including low friction material co-operating with a pin or seat, i.e. a watch type bearing including pièces of hard matériels such as diamond, ruby, sintered Carbide or Steel and co-operating pin or seat 01126, devices of appropriate material. In this case the connection is subjectto apressure instead of a tension as wîth the torsional means.

In the embodiment shown in Fig. 1 the viscosimeter is of Couette type and 5 includes a the vessel K supported by a motor shaft and the measuring body Mis to be dipped into the liquid inside the vessel. The measuring body M is rigidlyconnected to the spindle 4. The magnets of this embodiment are concentricallyarranged and axialiy magnetised. Consequently the co-operation between themagnets or rather the repulsion forces try to push the spindle downwardly io causing a tension in the torsion string 5. The string however prevents any axialdisplacement of the spindle 4 and the resuit is that a balance is reached and thespindle is held exactly in the centre of the device.

The embodiment according to Fig. 2 differs from the one according to Fig. 1 in 15 that there is no motor for rotating the vessel K, but otherwise the interactionbetween the magnets and the string is equal with that of Fig. 1.

Fig. 2b shows another embodiment, and in this the magnets are arranged in away similar to that of Fig. 1 and 2 but the support and spindle arrangement is 20 inverted. Consequently the magnets of the support and of the spindle act in theopposite direction and strive for lifting the spindle out of the support. The torsionstring 5 prevents any axial movement upwardly of the spindle and the co-operating magnets of the support and the spindle create a stabilising force. 25 Fig. 2c differs form the just described embodiment in that the magnets are radially magnetised. The magnets 1 of the support are directed magnetically in adirection opposite to that of the magnets 2 of the spindle 4. The magnets 1 and2 of Fig. 2c try to repel each other but as the support does not give wayoutwardly and the spindle does not give way inwardly the combined forces resuit 3o in a position of equilibrium, which per se is unstable, but as the magnets 1 and 2 are mutually axialiy offset there appear an axial force component trying to axialiy displacing the spindle 4 relatively to and out of the support 3. This lifting force is counteracted by the unyielding torsion string 5 and the resuit is that the spindle 7 01 126,. is kept stable in the centre of the support in a position defined both radially andaxially.

In Fig. 3 is illustrated an embodiment utilised at a viscosimeter of Couette type, 1. e. similar with the viscosimeter according to Fig. 1, but the magnets Γ of thesupport 3’ and the magnets 2’ of the spindle 4’ are arranged in an axialarrangement. The magnets T and 2’ are axially displaced and otherwise sooriented that the magnet pôles are in a repulsion state. The stationary magnetsT try to push the spindle with the movable magnets 2’ out of the support 3’ butthis is counteracted by the string 5' connecting the spindle 4’ to the support 3’thereby keeping the spindle in an axially defined position as well as in a radiallywell defined position.

The embodiment according to Fig. 4 illustrâtes a viscosimeter comparable withthe one according to Fig. 2 but as in the embodiment according to Fig. 3 themagnets are arranged in an other way than in the embodiment according to Fig. 2. According to Fig. 4 the magnets 1” and 2” are arranged in parallel with eachother and axially displaced. In this case however the pôles of the magnets arearranged in a way opposite to that according to Fig. 3, namely so that thestationary magnets 1” try to attract the movable magnets 2” and so to say try topull the spindle 4” out of the support 3”. As in the other examples the torsionstring 5" counteracts the axial displacing of the spindle.

The examples given in Fig. 1 to 4 are the once now preferred especially forinstruments of the type shown.

Fig. 5 schematically shows no less than ten different configurations withcombinations of radially and axially magnetised magnets for radial passivemagnet bearing devices, which can be used for the bearing device according tothis invention. In Fig 5 no connecting means are shown as the positioning ofsaid devices dépends on the selected off-set direction and the type ofconnecting device chosen. 8 01126.

Item one is a combination with axially magnetised magnets and it is clerarlyvisible that the inner and outer magnets are mutually offset in axial direction.

Item two is combination of axially and radially magnetised magnets.

Item three is a combination of opposing axially magnetised magnets where the s movable magnets are axially displaced relatively to the stationary ones.

Item four is an other example of magnets magnetised similar with the ones ofitem two but where the movable magnets are placed beyond the stationaryones.

Item five is an arrangement similar to the one according to Fig. 4 that is withw attractive arrangement of the magnets.

Item six shows an arrangement with oppositely directed radially magnetisedmagnets.

Item seven shows the opposite to item two that is the movable magnets areaxially magnetised whereas the stationary ones are axially magnetised. 15 Item eight is an example where the movable and the stationary magnets aremagnetised unidirectional.

Item nine is comparable with item seven but the movable magnets aremagnetised in opposite directions and positiorred beyond the stationary ones.Item ten is comparable with item six but in this case the stationary and the 2o movable magnets are acting in different axial planes. *

The embodiment according to Fig. 6 includes a support or stand 13 in which avertical bore 7 is arranged. Around the bore 7 there are stationary magnets 11and inside the bore 7 a spindle device 14 carrying a number of magnets 12 co- 25 operating with the stationary magnets 11 of the stand 13. The spindle 14 isprovided with a central bore 8 and has at its upper end projecting above thestand a connection 9 for a torsion string or wire 15 extending along the centralbore of the spindle and so adapted that the spindle is kept in a defined axialposition relatively to the stand by the influence of the magnets 11 and 12, 3o respectively, at the stand and the spindle so that the resulting force strives to push the spindle upwardly, i.e. out of the bore of the stand. The torsion wire this way will détermine the axial position and create a stabilising force holding the spindle in the centre of the stand bore 8. 9 011262

At its upper end the spindle 14 has a conical head 10 adapted to be received ina complementary shaped recess R of a measuring vessel carrier or holder.

The spindle 4 in the illustrated embodiment is provided with a driving means Dadapted to give the spindle a controlled limited rotational movement and asensor means S also connected to the spindle and influencing a computerdevice for determining the properties of a liquid filled into the vessel K.

As a torque résistance of the torsion string or wire 5 is known and constant andalso the force exerted by the driving means it is by means of the sensing devicein co-operation with the computer possible to détermine the properties of theliquid in the vessel.

The embodiments discussed above are generally intended for instruments andthe like where the rotatable part rotâtes over a fraction of a turn or just a fewturns. As mentioned above it is however possible to utilise a torsion means, astring or the like which allows a large number of rotations if this is required. If thedevice is intended for a use where the rotatable part is intended to rotate manyturns, the axial positioning against the axial thrust from the co-operatingmagnétos, normally is reached by means of an axial bearing e.g. of watchspindle type, where a pin is received in a recess in a piece of a hard materialsuch as diamond, ruby, sintered Carbide or the like or of the type where aspherical body attached to the one part is received in a part spherical seat at theopposite part. Such axial bearings, similar with the torsion string or tape,naturally, are localised in such a way that the rotational axis thereof is congruentwith the rotational axis of the bearings device as a whole. In the axial bearingtypes the bearing is subjected to an axial thrust or pressure, the contrary to thetorsion means types where a tensional force acts along the torsion means.

The embodiment according to Fig 7 shows one example of a device where there is no torsion means but instead a pin 5x cooperating with a bearing piece 6x of saphire, ruby, diamond or the like hard material. The magnets are magfnetised 10 01 1-26,- in such a way that the axial force component thereof pushes the inner part 4upwardly towards the bearing piece 6x. The pin being rather weak has as onlypurpose to stabilize the inner part 4 axially. From the same figure can also beseen a holed lid like lïd like ond closure of the outer part 7 serving as an 5 abutment preventing accidentai axial movements of the inner part.

In the embodiments shown there are at least two pairs of magnet units, axiallyseparated from each other. By arranging two sets of axially spaced magnet unitsas disclosed radial aligning or stability is achieved. If there was only one set of io magnet units the rotatable part could hâve a tendency to rock or swing, meaningthat the axis of rotation would deviate and rotate around the intendedgeometrical axis. By arranging two axially spaced magnet sets the axis ofrotation is stabilized and kept aligned with the geometrical axis. 15 The magnet units in each set can be similarily oriented magnetically, i.e. so thatthey bias the rotatable part together in the same direction. They can, however,also be oriented opposite to each other so that they bias the rotatable part inopposite directions. In the latter case, it is important that the biasing force of theone set of magnet units overrides the biasing force of the other set of magnet 20 units and this is a necessity both in the case the units work inwardly against each other or outwqrdly from each other. In order to keep the rotatable part in itsintended position, there is, according to the invention, arranged a connecctormeans which positions the rotatable part either by means of a torsion device oran pin bearing against a hard material or the like. 25 ,n instruments where a rotatable part is supported by a connector especially bya torsion string balancing the axial force from the magnet units, the rotatablepart 3 could by accident be pushed inwardly so that it not only reaches the nullpoint but also passes this equilibrium position. The resuit would be a total 30 wrecking of the instrument. In order to reduce the risk for such accidents it is suggested to arrange a second connector means acting in a direction opposite to the one of the first connector means and this means could be of torsion means type or hard material bearing type. The most convenient way is to attach 11 0112ύ, one connector means at each axial end of the rotatable part but is in many cases more convenient to arrange at the one axial end only of a rotatable part, a combined torsion string and hard material bearing by mounting the string inside a tube like device at either end having a seat or surface co-operating with a hard 5 material piece. In this way the opposite end of the rotational part is free forattaching measuring vessels or the like.

To reduce the risk for, by mistake, pushing the rotatable part so that it passesthe null point and disappears into the stationary part, it is also possible to io arrange mechanical abutments either at the stationary or the rotatable part or atboth and design the abutments so that the rotational part after a small axialdisplacement is prevented from entering the stationary part alternatively toleave the stationary part if the connector means fails. 15

Claims

12 Γ, < Z b 01 1 CLA1MS

1. Bearing device of magnet type particularly for use in instruments and like, allowing a rotational movement of one part relatively to another part and including at least one magnet unit at each part, said magnet units creating magnetic fields, the forces of which balance or stabilise the parts relatively to each other especially in directions radial to the axis of rotation of the one part, io wherein the magnet unit or units (2) of the one, preferably rotatable, part (4) isso localised and arranged relatively to the magnet unit or units (1) of the other,preferably stationary, part (3) that the interacting fields of force of the magnetunits (1, 2) of the two parts - besides radially acting balancing or stabilising forcecomponents - create force components resulting in an axial displacement force 15 biasing the one, preferably rotatable, part (4) in the one axial direction relativelyto the other, preferably stationary, part (3) and wherein at least one axially actingmechanical positioning means (5) is mounted to connect the one part with theother part said positioning means neutralising or counteracting the axial forcecomponent biasing the rotatable part being an axially at least unidirectionally 20 essentially stable, at least partially rotatable connector,characterized in that the at least unidirectional stable connector is a torsion means such as a torsionwire or string (5) secured to the rotational part at and extending along therotation axis thereof, said torsion means allowing at least limited rotation in 25 either rotational direction and preventing displacement in at least the one axialdirection caused by the axial repelling force component.

2. Bearing device according to claim 1, characterized in that an unidirectional stable torsion means is attached between, on the one 30 hand, each axial end of the rotatable part and extending axially outwardly therefrom; and on the other hand, appropriate securing points at the stationary part, the one torsion means preventing axial displacement of the rotatable part in 13 01 i. 2 ό z. a direction opposite to the displacement preventing direction of the other torsionmeans.

3. Bearing device according to claim 1or2 characterized in that 5 mechanical axial displacement preventing abutment portions are arranged at theone and/or other part, said portions upon engagement preventing thedisplacement of the rotatable part relatively to the stationary part beyond aminimum displacement. io 4. Bearing device according to claim 1,2 or 3, characterized in thateach magnet unit includes a number of axially magnetised magnets (2)preferably concentrically arranged.

5. Bearing device according to claim 1,2 or 3, characterized in that 15 each magnet unit includes a number of radially magnetised magnets, preferably concentrically arranged

6. Bearing device according to claim 1, 2 or 3, characterized in thatthe one part and the other part (4, 3) are provided with axially in both directions 20 facing abutment portions preventing axial displacement beyond a pre setdistance in both the axial directions. ;

7. Bearing device according to any of daims 1-6, characterized in thatat least two axially spaced sets of magnets or magnet units (2,1) are arranged 25 at the one or rotatable part (4) as well as at the other or stationary part (3), theco-operating or counteracting magnetic force fields thereof being arranged togive an excess of axial biasing force in the one direction, this excess force beingcounterbalanced by the mechanical positioning means (5).

8. Analyses instrument characterized in that it includes a bearing device according to any of the daims 1 to 7. 14 01 1 2 6

9. Method for determining rheological properties of a liquid, characte rizedin placing the liquid in a vessel (K) of a analysisinstrument according to claim 8 and recording and analysing the readings of theinstrument.

10. Method according to claim 9, characterized in that the analyses isperformed by means of a computer program.